Photographic emulsion containing dibenzoxacarbocyanines



Patented June 12, 1934 PHOTOGRAPHIC EMULSION CONTAINING DIBENZOXACARBOCYAN'INES Leslie G. S. Brooker, Rochester, N. Y., assigner to Eastman Kodak Company, Rochester, N. Y., a

corporation of New York Application February 20, 1932, Serial No. 594,381

s claims.

This invention relates to a photographic emul- .sion sensitized by a new class of photographic sensitizing dyes,'and more'particularly to gelagraphic art that in order to render photographic 4/3\/O emulsions, such as gelatino-silver-halide emull I zo-CH, 60

sions, sensitive to substantially all of the visible \1/ rays of the spectrum, it is necessary to treat the 5/\/ N emulsions, either by overcoating or by admixture 1 with the emulsions themselves, with a compound 6 7 8 which extends or enhances the sensitivity of the 65 emulsions to light beyond their natural sensitivity. A Many dyes suitable for thispurposehave been The numbering given is that used irr-Richters previously described in the literature, such for Lexikon der Kohlenstoff Verbindungen and instance as pseudocyanine, sensitol red, kryptocyalso in Chemical Abstracts. The l-methyl-aanine, thiocarbocyanine, and others. Additional naphthoxazole may be prepared from Z-amno-l- 70 ones have also been described in my previously naphthol in a manner similar to that described by -fledv (3o-pending applications, Such for instance MlChel and GlaIldInOllgIl (10C. Clt.) 'OI the SO- as thenaphthocarbocyanines described in my meriC 2-methyl-maphthoxazole.

U. s. Patent No. 1,846,300 of Feb'. 23, 1932 and This base will yield dibenzoxaoarbooyanine my eppueetien serial No. 435,105 iiied Merch 12, dyes, the formation of which probably takes place 75 1930. The dibenzexeeerbeeyenines, described in as follows: rst. the base is converted into a the instant application were likewise described Sultabe alkyl Quaternary salt, Such as the methoin my U S patent No. 1,846,300 of Feb. 23 1932, er etho-p-toluenesulfonate or the methiodide or in which it was related that'nstead of employing ethiodide, by heating the base with a suitable suba methylnaphthothiazole as the starting material Stance Such as methyl p'tfluenesulfo'nate 01' 80 for producing the dibenzocarbocyanine, one could methyl lodlde' under appropriate condltlons for replace the sulphur in the thiazole by oxygen and Instance produce a dibenzoxacarbocyanine by using the I, methylnaphthoxazole as the starting material. /0 /O 3J These dibenzoxacarbocyanines sensitize a gela- 1 x 85 tino-silver-halide emulsion containing them to "CHZ CH3 the yellow-green portion of the spectrum, con- \N% \N/ tributing a maximum sensitivity at approximate- R/ \X 40 ly 5550 Angstrom units. n 90 l It is an object, therefore, of this invention to provide a phtgaphiC emulsion Such as gelatno" 2mfthylnnphthoxazole 2-moihyl--naphthoxazole silver-halide emulsion, which contains a new alkyl Quaternary Salt sensitizing dye belonging to the class of dibenzoxa- CaIbOCYaniDBS and t0 prepare photographic elewhere R is an alkyl group such as methyl or ethyl, 95

4ments having a transparent SllpDOIt @Dated With and X is a suitable acidic radical, such as psuch anv emulsion. Other objects will occur to tomenesulfonate er iodide,

those skilled in the art upon a further perusal This quaternary salt. forinstance,2methy1 of this specication. naphthoxazole metho-para-toluenesulfonate (2 The compound known as 2-methyl--na`phmols'.) is then heated with ethyl orthoformate 100 tino-silver-halide emulsions sensitized with a new class of dyes known as the dibenzoxacarbocyanines and to photographic elements comprisingv such an emulsion.

It has been known for some time in the photothoxazole, for instance, was rst described, together with its method of preparation, by Bttcher (Ber,1883, 16, 1933). A somewhat dierent method of preparing this base was later described by Michel Sz Grandmougin (Ben, 1892, 25, 3429). The structure of the 2methyl--naphthoxazole is as follows:

' methenyl group,

`(1 mol.) in the presence of anhydrous pyridine whereupon the dye is formed. The reaction may be represented as follows:

nary salt In practice abetter yield of dye is obtained if .an excess of ethyl orthoformate is employed over that theoretically necessary. Other ortho-esters offormic acid, such as trimethyl orthoformate, may, of course, be used. It is desirable to number the dye molecule in the above fashion in order that this numbering will be in accord with that given to the sulphur containing dye named', for' instance, in my application Serial No. 337,177. The nal name for a dye of this type therefore becomes 2,2dialkyl3:4:3 :4dibenzoxacarbo cyanine salt. In the above formulae, R may be similar or dissimilar Aalkyl radicals depending upon whether the naphthoxazole quaternary salt contains only the one alkyl radical or whether twol portions of the salt are employed each havinga diiferent alkyl radical.

After the formation of the dye, it may be isolated and purified by ordinarychemical methods, or it may be converted into another salt, usually a less soluble one, by double decomposition in the ordinary fashion. For instance the p-toluenesulfonate of a dye may be converted into a bromide by treatment, in solution, with a soluble bromide, such as sodium bromide. The acid radical finally employed may be one such as a halide, perchlorate, nitrate, acetate, p-toluenesulfonate or in fact any salt forming acid radical which will not greatly decrease or destroy the sensitizing properties of the dye. X in the above formulae of the carbocyanines may represent any of these acid radicals.

` In the dyes the two naphthoxazole 'nuclei are linked together by a chain comprising three carbon atoms. Since the :CI-I- group is called the the chain :CH-CH=CH may be called a trimethenyl chain. Cyanine dyes containing this trimethenyl chain are commonly called carbocyanine dyes.

The diagrammatic spectrograms constituting the accompanying drawing illustrate the region of the spectrum to which the specic dyes herein disclosed will sensitize a gelatino-silver-halide emulsion and theextent of the sensitization-at Various Wave lengths. The figures of the drawing and the dyes, the sensitizng properties of which vthey illustrate, are as follows:

, cyanine bromide.

Examples of specific methods by which these dyes may be prepared are as follows, but it will of course be understood that these are not limitdibenzoxacarbocyanine salt ing but merely illustrating the manner of effecting the broad principles of my invention.

6.1 g. 2-Inethyl--naphthoxazole is heated with 6.2 g. methyl p-toluenesulfonate for 6 hours at about 160 C. During a further 15 hours heating at 130-140 C. the product solidies to a brownish solid. The product, substantially 2- methyl -naphthoxazole metho-p-toluenesulfonate, is boiled under reflux with anhydrous pyridine (40 cc.) and ethyl orthoformate (5.5 cc., 100% excess). A reddish orange color forms rapidly and refluxing is continued for 45'minutes. A hot solution of excess of potassium bromide (20 g.) in water (100 cc.) is added to the reaction mixture, and the dye is rapidly precipitated as the bromide. The crude vdye may be freed from impurities by boiling it successively With water and then with acetone, and then recrystallizing it from methyl alcohol, whereupon it is obtained as a mass of red silky needles which give an orange solution in the solvent,

9.15 g. Z-methyI-naphthoxazole is condensed with 10 g. ethyl p-toluenesulfonate by heating for 6 hours at 160-180 C. and for 15 hours at tiallyv Z-methyl--naphthoxazole eth0 p-tolueneq l sulfonate may be used without purification. It

is reiluxed for 45 minutes with anhydrous pyridine (30 cc.) and ethyl orthoformate` (8.2 cc., 100% excess). The dye is then precipitated as the bromide by adding an excess of a Warm solution of potassium bromide (20 g.) in water 1 (100 cc.) After ltering, the dye may be washed with water and then with hot acetone and finally recrystallized from methyl alcohol, in which it gives an orange solution. It is obtained as n reddish needles.

In the same manner that the 3:4:324 dibenzoxrcarbocyanine is prepared, one may prepare the 526:5z6dibenzoxacarbocyanine, if one were to start with the 1methyla1pha naphthoxazole instead of the 2-methyl-nanh ithoxazole as above described. The structure of the base is given below, as well as that of an oxacarbocyanine dye derived from it.

l methyl-a-naphthoxazole The numbering is that used in' my applicationV 2-nitro-1-naphthol is rst prepared (see,for

instance, Hodgson & Kilner, J. C. S. 1924, 125,:

807). This compound is then reduced to the corresponding 2-amino-l-naphthol, using tin and hydrochloric acid as recommended by Liebermann & Dittler (Ben, 1874, 7, 240; Liebermann, Ann., 1876, 183., 246). The hydrochloride of the base is then heated with acetic acid and sodium acetate for several hours in a similar fashion to that prescribed for the preparation of '2-methyl--naphthoxazole by Michel & Grandmougin (Ber., 1892,` 25, 3429). The excess f acetic .acid is then slowly distilled off and the residue is finally distilled in vacuum, using an oil bath to heat the reaction flask. The base distills over and is purified by dissolving the distillate in ligroin, allowing a solid impurity to crystallize out rst, and then isolating the base from the mother liquor. The l-.methyl-a-naph-v thoxazole is obtained as a low melting solid.

nFor the preparation of the dyes the base is converted into a quaternary salt-,such as the.

methyl p-toluenesulfonate or the ethiodide in the usual way. The quaternary salt is then condensed with ethyl orthoformate in the presence of anhydrous pyridine as described for the isomeric dyes derived from Z-methyl--naphthoxazole.

Eample III afmass of crystals. This is then refluxed with 25 parts of anhydrous pyridine and 1.6 'parts of ethyl orthoformate (300% excess of the latter the yield is improved by taking an excess of the ester). Within a few minutes the dye begins to separate, the p-toluenesulfonate of the dye being very sparingly soluble in pyridine, hot or cold. After 30 minutes reiluxing, the reactionV mixture is allowed to cool, and thel dyeis then filtered off and washed with cold pyridine and then dried. The yield is about 1.3 parts. This dye is 2,2' dimethyl5 6 5' :6'dibenzoxacarbo cyanine petoluenesulfonate.

The dye may be converted into the bromide by dissolving it in boiling methyl alcohol and adding an excess of an aqueous solution of an alkali bromide, such as potassium bromide, to the alcoholic solution. The bromide of the dye is almost insoluble in alcoholic-aqueous solution in the presence of a large excess of bromide ions and may be ltered off, washed with water, and then purified by recrystallization from ethyl or methyl alcohol. This dye 'is called 2,2-dimethyl- 5 :6 2 5 :6dibenzoxacarbocyanine bromide. If potassium iodide is used in place of potassium bromide then the still less soluble dye iodide is formed. The bromide of the dye crystallizes from methyl alcohol as a felted mass of hairlike crystals, reddish-orange in color. The solution of the dye in the solvent named is orange.

Example I V If 1.1 parts of ethyl p-toluenesulfonate are used instead of the 1.05 parts of methyl p-toluenesulfonate used in the preceding example, and the two components are heated on the steam bath for 24 hours, l-methyl-a-naphthoxazole etho-p-toluenesulfonate is produced. This salt is condensed with ethyl orthoformate in boiling pyridine solution in the same manner described in the preceding example, using 10 parts of pyridine and 1.6 parts of the ortho-ester. After 30 minutes refluxing the dye 'is precipitated from the deeply colored solution by adding thereto an excess of an aqueous solution of potassium iodide. The dye is ltered off, washed with water and with acetoneand is puried by several recrystallizations from methyl alcohol, in which it gives an orange solution. The 2,2'diethyl5:6:5:6' dibenzoxacarbocyanine iodide is obtained in beautiful garnet-red crystals with a'strong blue reex.

The naphthalene nuclei in both the mu-methyl naphthoxazoles may be left unsubstituted or they may be substituted.

In the preparation of emulsions containing these photographic sensitizers, it has been found that the dye may be dissolved in methyl alcohol and a volume of solution diluted with water and containing from 5 to 100 milligrams of dye added to 1000 cc. of emulsion. While it may not be necessary to add some of the sensitizers in a large amount, it may be necessary to add others in amounts larger than those given above; generally, about 10 to 20 milligrams is suilicient to obtain the maximum sensitizing eiect with a dye having good sensitizing power. The more powerful dyes, however, may require much less. 'I'he regulation or adoption of the most economical proportions will be apparent to those skilled in the art upon observing the sensitizing power of the particular dye for the particular emulsion to be formed. The above examples are, therefore, illustrative andnot to be understood as limiting the invention in any sense, as it will be apparent that these dyes may be incorporated by other methods in many of the photographic emulsions customarily employed in the art, such for instance as by bathing the plate or lm, upon which the emulsion has been coated, in a solution of the dye in an appropriate solvent although this method of incorporating the dye in the emulsion is not preferred over that above described. Obviously the claims are all intended to cover any combination of vthese dyes with a photographic emulsion whereby the dye exerts a sensitizing effect upon the emulsion.

What I claim is:

1. A photographic gelatine-silver-halide emul- 5 sion containing a. dibenzoxacarbocyanine salt.

2. A photographic gelatino-silver-halide emulsion containing a. dialkyl-dibenzoxacarbocyanine salt.

3. A photographic gelatino-silver-halide emulsion containing a dialkyl-dibenzoxacrbocyanine bromide.

LESLIE G. vs. BROOKER.l 

